The present invention relates to fungicidal two- and three-component mixtures based on metalaxyl having an R-enantiomer content of more than 70% by weight, and to the use thereof in controlling and preventing Oomycetes infestation. The metalaxyl component is called active ingredient I.
The following fungicides may be used as the second component II of the mixture:
IIA) mancozeb;
IIB) chlorothalonil;
IIC) a copper salt, for example CuCO3, CuSO4, Cu(OH)2.CUCl2, especially Cu(OH)2;
IID) folpet;
IIE) fluazinam [=3-chloro-N-(3-chloro-5-trifluoromethyl-2-pyridyl)-xcex1,xcex1,xcex1-trifluoro-2,6-dinitro-p-toluidine]; and
IIF) cymoxanil, which can be used either on its own or in admixture with one of the above-mentioned components IIA to IIE (three-component mixtures).
More specifically, the invention relates to mixtures comprising metalaxyl having an R-enantiomer content of more than 85% by weight, preferably of more than 92% by weight, and especially containing pure R-enantiomer that is substantially free of S-enantiomer.
Metalaxyl of the formula 
has an asymmetric *C atom and can be resolved into the enantiomers in customary manner (GB-P.1 500 581). Since 1975 it has been known to those skilled in the art that the R-enantiomer is far superior to the S-enantiomer in terms of fungicidal action and is in practice regarded as the true mechanism of action. Commercial metalaxyl is available in the form of the racemate. Likewise, mixtures of metalaxyl racemate with mancozeb, chlorothalonil, copper preparations, folpet, fluazinam or cymoxanil have become known commercially or otherwise. There has in the past never been any practical necessity to resolve the racemate, of which half consists of the desired R-enantiomer.
It has now been found, completely surprisingly, that R-metalaxyl in pure or more than 70% form, in admixture with the fungicidal components IIA to IIF, achieves a synergistically enhanced action which in some cases exceeds that of the prior-known mixtures based on the racemate by a factor of 10. Given that half of the racemate consists of R-enantiomer, factors of approximately 2 or, at most, 3 were to be expected.
With this completely unexpected result, the present invention constitutes a very considerable enrichment of the art and represents a possible means of reducing in an environmentally protective manner the total amount of fungicides used for controlling Oomycetes on plants.
In addition to the two-component mixture I:II, the present invention relates also to a method of controlling fungi, which comprises treating a site, for example a plant, that is infested by or threatened with infestation by fungi with, in any desired sequence or simultaneously, a) component I and b) the active ingredient of formula II.
Advantageous mixing ratios of the two active ingredients are I:II=from 10:1 to 1:100, preferably I:II=from 5:1 to 1:30. In many cases, mixtures in which the mixing ratio of the active substances I:II is from 1:1 to 1:20, for example 2:5, 1:4, 1:8 or 1:10, are advantageous.
The active ingredient mixtures I+II according to the invention have very advantageous curative, preventive and systemic fungicidal properties for protecting cultivated plants. The active ingredient mixtures of the invention can be used to inhibit or destroy the micro-organisms which occur on plants or on parts of plants (the fruit, blossom, leaves, stems, tubers or roots) of different crops of useful plants, while at the same time parts of plants that grow later are also protected against such microorganisms. This applies especially also to microorganisms that have developed reduced sensitivity to metalaxyl.
The active ingredient mixtures of formulae I and II are generally used in the form of compositions. R-metalaxyl (formula I) and the active ingredient of formula II can be applied to the area or plant to be treated simultaneously or in immediate succession, if desired together with further carriers, surfactants or other application-promoting adjuvants customarily employed in formulation technology.
Suitable carriers and adjuvants can be solid or liquid and are the substances ordinarily employed in formulation technology, e.g. natural or regenerated mineral substances, solvents, dispersants, wetting agents, tackifiers, thickeners, binders or fertilisers.
A preferred method of applying an active ingredient mixture comprising at least one of each of the active ingredients I and II is application to the parts of the plants that are above the soil, especially to the leaves (foliar application). The frequency and rate of application depend upon the biological and climatic living conditions of the pathogen. The active ingredients can, however, also penetrate the plant through the roots via the soil (systemic action) if the locus of the plant is impregnated with a liquid formulation or if the substances are introduced in solid form into the soil, e.g. in the form of granules (soil application).
The compounds of the combination are used in unmodified form or, preferably, together with the adjuvants conventionally employed in formulation technology, and are therefore formulated in known manner e.g. into emulsifiable concentrates, coatable pastes, directly sprayable or dilutable solutions, dilute emulsions, wettable powders, soluble powders, dusts, granules, or by encapsulation in e.g. polymer substances. As with the nature of the compositions, the methods of application, such as spraying, atomising, dusting, scattering, coating or pouring, are chosen in accordance with the intended objectives and the prevailing circumstances. Advantageous rates of application of the active ingredient mixture are normally from 50 g to 1800 g of active ingredient (a.i.) per hectare, preferably from 100 g to 1000 g a.i./ha. Mixtures of R-metalaxyl (I) with mancozeb (IIA) are advantageously employed at rates of application of from 100 g to 120 g of I and 1600 g of IIA.
The formulations are prepared in known manner, e.g. by homogeneously mixing and/or grinding the active ingredients with extenders, e.g. solvents, solid carriers and, where appropriate, surface-active compounds (surfactants).
The agrochemical compositions generally comprise 0.1 to 99%, preferably 0.1 to 95%, of active ingredients of formulae I and II, 99.9 to 1%, preferably 99.9 to 5%, of a solid or liquid adjuvant and 0 to 25%, preferably 0.1 to 25%, of a surfactant.
Whereas commercial products will preferably be formulated as concentrates, the end user will normally employ dilute formulations.
Suitable target crops are especially potatoes, vines, hops, maize, sugar beet, tobacco, vegetables (tomatoes, paprika, lettuce, etc.), and also bananas, natural rubber plants, as well as lawn areas and ornamentals. Other plants threatened by downy mildew have become known inter alia from the literature relating to metalaxyl.